Just typos:
On Mon, Oct 16, 2023 at 08:27:52AM -0500, Michael Roth wrote:
> From: Brijesh Singh <brijesh.singh@xxxxxxx>
>
> Implement a workaround for an SNP erratum where the CPU will incorrectly
> signal an RMP violation #PF if a hugepage (2mb or 1gb) collides with the
> RMP entry of a VMCB, VMSA or AVIC backing page.
>
> When SEV-SNP is globally enabled, the CPU marks the VMCB, VMSA, and AVIC
> backing pages as "in-use" via a reserved bit in the corresponding RMP
> entry after a successful VMRUN. This is done for _all_ VMs, not just
> SNP-Active VMs.
>
> If the hypervisor accesses an in-use page through a writable
> translation, the CPU will throw an RMP violation #PF. On early SNP
> hardware, if an in-use page is 2mb aligned and software accesses any
> part of the associated 2mb region with a hupage, the CPU will
"hugepage"
> incorrectly treat the entire 2mb region as in-use and signal a spurious
> RMP violation #PF.
>
> The recommended is to not use the hugepage for the VMCB, VMSA or
s/recommended/recommendation/
s/the hugepage/a hugepage/
> AVIC backing page for similar reasons. Add a generic allocator that will
> ensure that the page returns is not hugepage (2mb or 1gb) and is safe to
"... the page returned is not a hugepage..."
...
> +struct page *snp_safe_alloc_page(struct kvm_vcpu *vcpu)
> +{
> + unsigned long pfn;
> + struct page *p;
> +
> + if (!cpu_feature_enabled(X86_FEATURE_SEV_SNP))
> + return alloc_page(GFP_KERNEL_ACCOUNT | __GFP_ZERO);
> +
> + /*
> + * Allocate an SNP safe page to workaround the SNP erratum where
> + * the CPU will incorrectly signal an RMP violation #PF if a
> + * hugepage (2mb or 1gb) collides with the RMP entry of VMCB, VMSA
> + * or AVIC backing page. The recommeded workaround is to not use the
"recommended"
> + * hugepage.
> + *
> + * Allocate one extra page, use a page which is not 2mb aligned
> + * and free the other.
> + */
> + p = alloc_pages(GFP_KERNEL_ACCOUNT | __GFP_ZERO, 1);
> + if (!p)
> + return NULL;
> +
> + split_page(p, 1);
> +
> + pfn = page_to_pfn(p);
> + if (IS_ALIGNED(pfn, PTRS_PER_PMD))
> + __free_page(p++);
> + else
> + __free_page(p + 1);
> +
> + return p;
> +}
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
